Bonn — Bipartisanship is the new American buzzword at the strategic arms reduction talks (START) in Geneva. The Republican-Democratic togetherness is producing a yeomanlike plowing ahead in the START talks that is noteworthy in this time of embittered Soviet-American relations.
It is not yet producing any positive response from Moscow, however, according to information reaching NATO countries from the Geneva negotiations.
By now the United States has spelled out its basic ''build-down'' proposal in this fall's fifth round of talks, with the last segment - bombers - having been presented Oct. 25. The two delegations have also drafted annexes on counting rules and definitions and have begun discussing a verification annex.
The build-down is a bipartisan idea that was initially advanced on the MX intercontinental missile and related strategic issues. It is described by a proponent as ''a good basis for whatever party gets elected'' in fall of 1984.
To ensure that the build-down is pursued seriously by the Reagan administration, congressional arms control advocates like Wisconsin Democrat Les Aspin are essentially holding hostage biennial funding of the MX to support for the build-down. They adopted this tactic last summer after concluding that only bipartisanship could protect arms control against some future veto by an opposition party that could always muster the minimum of Senate seats needed to block two-thirds' ratification of any treaty.
As it is being presented to the Soviets in the October-November negotiating session in Geneva, the US proposal for a build-down would cut America's present 10,000 and the Soviet Union's present 8,800 strategic warheads and bombs to 5, 000 each, over a period of 10 years. It would also reduce the present Soviet lead in missile throw-weight (5.6 million kilograms to America's 1.8 million kilograms).
Both sides would be committed to a minimum 5 percent reduction per year and would have to pay for each new intercontinental ballistic missile (ICBM) warhead. They would have to pay for every two new submarine-launched ballistic missile (SLBM) warheads they deployed by destroying three old SLBM warheads. They could deploy new strategic bombers on a one-for-one substitution.
There would be no ''freedom to mix'' missiles and bombers - although some members of the American team are trying to devise a mathematical formula based on missile throw-weights and bomber loading weights that could give a common counting unit and thus allow freedom to mix.
So far Moscow has reacted negatively to the build-down idea - especially in a somewhat muddled Pravda attack on it a few days ago. The Soviets have not rejected the notion out of hand, however, and the American side hopes that after they have digested the new idea the Soviets will see it as a decent basis for negotiation.
In this context the current October-November round of talks and the next February-March round are seen as educational.
It is primarily through the Soviet negotiating team at Geneva that the concept of the build-down is being communicated to the Kremlin leadership.
The further hope of American arms controllers is that by next February the Soviets will have decided that the period preceding the US presidential election is the most favorable one for getting a deal with Washington. If so, they suggest, the build-down proposal should look much more attractive to Moscow than the original START proposal made by the US.
By contrast, the build-down concept calls for a more gradual reduction in ICBMs, the increasingly vulnerable but warhorse missiles that constitute almost three-fourths of today's Soviet arsenal but only one-fourth of the US arsenal.
Yet at the same time the build-down offers both sides incentives for moving away from MIRVed (multiple, independently targeted reentry vehicle) ICBMs and toward single-warhead missiles. MIRVs are ''destabilizing'' because they combine vulnerability with an accurate ''first strike'' threat.
This aspect of the build-down proposal could prove attractive to the Soviets in effectively ''penalizing'' not only the Soviet SS-18 heavy ICBM, but also the MX being developed by the US.
So far the Soviet Union is sticking with the START proposal it made prior to American introduction of the build-down. This is basically a ''SALT II minus'' position that would set overall ballistic missile warhead ceilings (11,400) and MIRVed ICBM warhead ceilings (680) lower than the 1979 SALT II limits.
At this point the START talks are burdened not only by the general deterioration in superpower relations and East-West confrontation over the imminent stationing of new NATO medium-range missiles in Europe, but also by confrontation over suspected Soviet violations of SALT II. Although the US never ratified the SALT II treaty, both sides have pledged adherence to it, and any suspected violations are raised in the bilateral standing consultative commission in Geneva.
This time around the Soviet Union has been far less willing to modify or explain suspect behavior than in any previous SALT I challenges. The specific issues involve radar that appears to be incompatible with the 1972 near-ban on antiballistic missile systems, and encryption of missile tests and possibly testing of a banned second new ballistic missile that might violate SALT II provisions.
Cutting the missile count SALT II US Soviet agreement build-down START proposal proposal Ballistic 14,600 5,000 11,400 missile warheads throwweight ICBM 820 limit or 680 warheads Soviet offer (MIRVed) (land-based) Bombers 120 400 120 (11 ALCMs* (20 ALCMs (10 ALCMs each) each) each) *Air-launched cruise missiles